Session 4. Chemical Changes and Conservation of Matter

Learning Goals

During this session, you will have an opportunity to build
understandings to help you:

Electrolysis

Refine and extend the particle model to develop an
atomic model of matter, and become familiar with some of the history
of the evolution of this model.

Recognize that chemical changes alter particles by
rearranging their component atoms into different combinations.

Recognize that matter is not created or destroyed
during chemical changes.

Recognize that the total number of atoms of each element
is conserved during chemical changes.

Video Overview

Where
does the weight go when we “lose weight”? What happens when iron rusts? Why are exploding stars able to turn other
elements into gold when the alchemists were not? In this session, we will
extend and refine the particle model by taking a closer look at the particles—atoms
and molecules—and will discover how the law of conservation of matter
applies to chemical changes.

Video Outline

We begin our investigation into the nature of particles by
observing that they have distinct sizes and shapes. Is this the explanation
for the “missing volume” of the shaken mixture of water and
alcohol in Session 3? Our hosts introduce the idea of chemical changes
and show an example of one way that they are distinguished
from physical changes.

Throughout this session, we visit Rebecca
Cituk’s classroom in Portsmouth, Rhode Island, where we listen as her sixth graders discuss
the differences
between chemical changes and physical changes and elements and compounds,
and perform a classic experiment to see if matter is conserved in a chemical
change. We return to the Science Studio where the interviewer uses a
different approach—manipulatives—to help Cameron, a fifth grade
student, explore a chemical change in which two clear liquids combine to
form an
opaque white solid. Both of these instances raise the following question:
What happens on the particle level that makes chemical
changes different from physical changes?

We then take a step back as science historian
Mimi Kim takes us on a historical journey through the development of
the modern science of chemistry,
beginning
with Étienne Geoffroy’s “affinity table” in
1718. Along the way, we revisit some of the experiments of Lavoisier
and Boyle
that broke substances down to their simplest components—elements—and
provided the first evidence for the law of conservation of matter.

Our
hosts pick up the journey, noting the contributions of Proust, Dalton,
Avogadro, and Sir William Robert Grove, whose electrolysis
of water experiment
they recreate as a real-world example of the law of fixed proportions.
We conclude the journey with Mendeleev’s organization of the
elements into the periodic table and ask astrophysicist Dr. Robert
Kirshner “Where
did the elements come from?”